1. Field of the Invention
The present invention relates to a continuously variable transmission. More particularly, the present invention relates to a continuously variable transmission having input and output pulleys that are adjustable in width and about which an endless torque-transmitting member passes, wherein the transmission ratio is variable.
2. Description of the Related Art
Continuously variable transmissions are generally known. The essential elements of such a transmission are shown in FIG. 3, which represents a section through the main structure of such a mechanism, that is, the speed-varying portion of a continuously variable transmission. A drive shaft 2 is driven by a drive motor (not shown) of a motor vehicle. Fixedly attached to the drive shaft, or constructed in one piece therewith, is a first conical disk 4 of a pair of conical disks that define a pulley 6, the other conical disk 8 of which is non-rotatably but axially movably connected with shaft 2. Also fixedly attached to drive shaft 2 is a backup ring element 10, between which and conical disk 8 are formed a pressure chamber 12, to which is admitted a torque-dependent hydraulic pressure, and an adjustment chamber 14, to which is admitted an hydraulic adjustment pressure. The admission of pressure medium into the chambers occurs through ports and corresponding throughbores in drive shaft 2 that are not individually illustrated.
An output shaft 22 is connected with a pulley and related hydraulic chambers in a manner similar to that of the drive shaft, whereby corresponding elements are provided with reference numerals that are higher by 20 than those for the drive shaft pulley. The pulleys 6 and 26 are spanned by an endless torque-transmitting member 40 that transmits rotation of drive shaft 2 to rotation of output shaft 22, and during deceleration it transmits rotation in the reverse direction. In the illustrated arrangement the spacing between the conical disks 4 and 8 is at a maximum, and that between conical disks 24 and 28 is at a minimum, so that the transmission produces the lowest possible transmission ratio, that is, it is in underdrive. When the spacing between conical disks 4 and 8 diminishes and the spacing between conical disks 24 and 28 correspondingly increases, the transmission crosses over the condition when the transmission ratio is 1, increasing to overdrive.
The construction, function, and control of such devices are known and therefore will not be further explained herein.
In continuously variable transmissions of the type such as that shown in FIG. 3, it is common, for various reasons, to make the oil supply for the transmission, that is the oil pressure, with which the oil requirements for lubricating oil are supplied, to be made dependent upon the motor rotational speed. A breakdown of the engine, thereby necessitating a towing operation, can result in unusually rapid rotation of the pulley 6, particularly for the illustrated underdrive condition of the transmission, whereas the pulley 26 that is connected to the vehicle""s driven wheels rotates slowly. The high rotational speeds can lead to damage to the motor-side pulley 6 and with it to associated components.
The invention has as an object to provide a solution to the above-mentioned problem.
Briefly stated, in accordance with one aspect of the present invention, a continuously variable transmission is provided that includes a drive side pulley and an output side pulley, and an endless torque-transmitting member that spans the pulleys, wherein the spacing between the conical disks that define each pulley is adjustable for varying the transmission ratio. A spring is provided that ensures that when the engine is stopped, and if necessary also if the transmission still has hydraulic medium under pressure, a force is exerted on the movable conical disk which takes the transmission, that is the variator, out of an underdrive condition during a towing operation, so that the rotational speed of the input side pulley 6 is decreased and the danger of damage is diminished, and in certain respects is completely avoided.
The invention can be employed everywhere that continuously variable transmissions can be in towed operation and in which there exists the danger of deficient lubrication from high rotational speeds of the input side pulley.